A coroner has recorded an open verdict at the inquest into the death of Russian tycoon Boris Berezovsky.
Mr Berezovsky, 67, was found on the bathroom floor of his Ascot home last year with a ligature around his neck.
Berkshire coroner Peter Bedford returned an open verdict, following two days of "contradictory" evidence.
He said he could not prove beyond all reasonable doubt that the businessman either took his own life or was unlawfully killed.
In 2012, the former Kremlin insider lost a £3bn ($4.7bn) damages claim against Chelsea FC owner Roman Abramovich.
The tycoon amassed a fortune in the 1990s following the privatisation of state assets after the collapse of Soviet communism.
'Impossible to say'
In summing up at Windsor Guildhall, Mr Bedford said: "I am not saying Mr Berezovsky took his own life, I am not saying Mr Berezovsky was unlawfully killed.
"What I am saying is that the burden of proof sets such a high standard it is impossible for me to say."
Earlier the court heard a detailed discussion about the knots tied in the scarf that was used as a ligature in Mr Berezovsky's death.
Home Office pathologist, Dr Simon Poole, who carried out a post-mortem examination, said there was nothing to indicate any other people were involved.
But Professor Bernd Brinkmann, who deals with hanging and asphyxiation cases, said the marks on Mr Berezovsky's neck could not have come from hanging.
He said they were "far away from the typical inverse 'V' shape" usually seen, whilst the congestion to his face was also not consistent with hanging.
He said he believed the businessman was strangled by someone else and then hanged from the shower rail in the bathroom.